As selective call receivers (such as pagers) have become smaller, it has become possible to package the electronics so that they can be comfortably worn on a user's wrist. Antennas used with these wrist worn receivers have often utilized a simple, single-turn loop antenna incorporated into the wristband of the device. Rivets, or similar fasteners, have been used to provide a series of regularly spaced openings in one of the wristband sections to accommodate the varying sizes of the human wrist. This also provided the electrical connection to close the loop when the wristband was fastened to the wrist.
Since a loop antenna's inductance is dependent upon its physical geometry (antenna diameter or length), the tuning of such a loop antenna varied with the wrist size. Consequently, substantial changes in the antenna's resonant frequency and changes in the corresponding receiver sensitivity resulted when the user adjusted the wristband for a comfortable fit. As a consequence, factory pre-tuning of such a wristband loop antenna was not possible. Skilled technicians were required to tune the antennas on the devices as they were being sold. Even after tuning the antenna properly, the device would malfunction if the user was inconsistent in strapping the device to the wrist.
Referring to FIG. 1, a typical prior art wristband loop antenna arrangement 26 generally used a non-stretchable, two-piece wristband. The receiver is located in a housing 12 to which two non-stretchable straps 14 and 16 are attached. Within each strap 14 and 16 is located an antenna 18 and 20, respectively. The antenna may be of various geometries although the typical shape is a flat, rectangular conductive wire or band. Attached to one end of the wristband strap 16 is a conventional buckle 24, which connects to one end of the antenna 20. In the other wristband strap 14, a series of regularly spaced holes are provided on a surface 22 to allow for adjustment of the wristband length. An eyelet (not shown) is often inserted into each of the holes to provide electrical connection with the antenna-18 within the strap 14.
Other antenna structures have also been proposed for use in wrist worn receivers although all have exhibited similar tuning problems. That is, as the geometry of the antenna loop was changed during adjustment, detuning of the antenna would occur. Also, reduced receiver sensitivity would result depending on the position of the wrist.
Thus, what is needed is a method of incorporating a loop antenna within an adjustable, flexible wristband that remains tuned, regardless of the position worn on the wrist.